Twisted-yarn-based
artificial muscles can potentially be used in
diverse applications, such as valves in microfluidic devices, smart
textiles, air vehicles, and exoskeletons, because of their high torsional
and tensile strokes, high work capacities, and long cycle life. Here,
we demonstrate electrochemically powered, hierarchically twisted carbon
nanotube yarn artificial muscles that have a contractile work capacity
of 3.78 kJ/kg, which is 95 times the work capacity of mammalian skeletal
muscles. This record work capacity and a tensile stroke of 15.1% were
obtained by maximizing yarn capacitance by optimizing the degree of
inserted twist in component yarns that are plied until fully coiled.
These electrochemically driven artificial muscles can be operated
in reverse as mechanical energy harvesters that need no externally
applied bias. In aqueous sodium chloride electrolyte, a peak electrical
output power of 0.65 W/kg of energy harvester was generated by 1 Hz
sinusoidal elongation.
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